Mined ores and other minerals usually contain impurities. Consequently, the desired ore or mineral product must be separated from the rest of the material, as mined. Talc, for example, exists in its natural state in rock formations in which it is typically associated, or combined with, dolomite and possibly also other minerals such as chlorite, quartz, pyrite, magnesite, calcite, feldspar, mica, etc., and mixtures thereof. In the production of talc, until recently, separation of the pure talc fraction from that of the impurities, hereinafter referred to collectively as "dolomite", had been effected by hand sorting, an arduous function that adds measurably to the time and cost of producing a product of commercial grade.
It has been determined that talc and dolomite exhibit differences of coefficients of sliding friction, and thereby, can be effectively separated on this basis. Apparatus disclosed in U.S. patent application Ser. No. filed 097,877, filed Sept. 17, 1987, and assigned to the assignee hereof describes a separating apparatus by which the materials, as mined, are induced by centrifugal forces to undergo sliding movement across a rotating surface whereby the talc and dolomite fractions are caused to move at different velocities such that they can be separately collected. Although the aforementioned apparatus is effective in separating talc from dolomite when the size of the particles to be separated is above about two inches in nominal diameter, its separating efficiency becomes significantly reduced on mixture particles whose nominal diameter is about two inches or less.
Separating apparatus utilizing inclined chutes having arcuately curved discharge portions are well known for classifying materials according to different properties. See, for example, U.S. Pat. Nos. 719,343, 753,591 and 753,592 to Langerfeld and U.S.S.R. Inventor's Certificate Nos. 496053 and 1165497. Such apparatus, as was heretofore known in the art, is, however, not dispositive of the problem addressed by the present invention. For example, the Langerfeld patents suggest utilization of an inclined surface of shallow extent whereby the particles of the mixture fractions are caused to achieve disparate speeds depending on their physical characteristics, such as specific gravity, form, size and/or the retardative nature of their surfaces in sliding along the inclined surface. The curved discharge portion at the end of each such incline serves simply to project the respective particles at different velocity-dependent trajectories wherein they can be collected in separate receiving bins.
U.S.S.R. Inventor's Certificate 496053, on the other hand, describes apparatus suitable for separating friable materials in which the angle of inclination of the inclined portion of the chute is made steep depending on the density and size of the particles being separated in order to permit the particles to achieve a velocity sufficient to impart a spinning motion therein wherein the particles will be fractured into smaller grains in contacting the chute surface prior to being discharged via a sifting surface as well as along disparate velocity induced trajectories to be, thereby, separately collected.
U.S.S.R. Inventor's Certificate 1165497 employs a steeply inclined chute having a section containing a concave-convex reversely curved discharge portion particularly adapted for separating relatively highly wetted particles wherein the smaller grain size fractions are caused by their being wetted to cling to the slide surface and thereby enable the collection of another mass-dependent material fraction.
It is to the amelioration of this problem, therefore, to which the present invention is directed.